> I've got an old screw pitch gauge that I inherited. There's no mfr's
> > name marked on it, just "Number 137".
>
> > the individual leaves are marked with two numbers each, but these
> > numbers are not reciprocals. The first number is always a small
> > integer which I presume is threads-per-inch.
>
> > the second number is always a decimal.
>
> > Any idea what the second set of numbers are?
>
> pairs of numbers are
> ~~~~~~~~~~~~~~~~~~~~
> 60 - 0.021
> 48 - 0.026
> 40 - 0.032
> 32 - 0.040
> 30 - 0.043
> 28 - 0.046
> 26 - 0.049
> 25 - 0.051
> 24 - 0.063
> 22 - 0.058
> 20 - 0.064
> 19 - 0.067
> 16 - 0.080
> 14 - 0.091
> 13 - 0.098
> 12 - 0.107
> 11 - 0.115
> 10 - 0.126
> 9 - 0.142
> 8 - 0.160
> 7 - 0.183
> 6 - 0.215
> 5 - 0.259
> 4-1/2 - 0.284 (sic)
> 4 - 0.320
>
> looking at the leaves, "depth of thread" in inches seems the most
> plausible to me. This item would date back to the 50's, I don't
> believe there was too much metric action in American machine shops at > that time. >
> I'd try _measuring_ the depths with a micrometer, but I don't know
> where to measure to/from. How is thread depth defined? And by the
> way, who sets the standards on how these things are measured?